They are stupid, she remarked, before talking about how to kill a person.

"It's easy... inject them with insulin," Ms Haines allegedly said during the 2009 conversation.

That is what Ms Haines is alleged to have done to two elderly residents at a NSW North Coast nursing home after learning they made complaints about her in 2014.

The South African born 49-year-old faced the NSW Supreme Court on Wednesday, accused of killing Isabella Spencer, 77, and Marie Darragh, 82, by injecting them with insulin when she was a nurse at St Andrews Village aged care.

Details of the conversation she had years earlier were aired during the first day of Ms Haines' trial and after she pleaded not guilty to two counts of murder.

Ms Darragh and Ms Spencer were both found in comatosed states in the early hours of May 10, 2014 at the St Andrews facility in Ballina.

It was initially thought the pair had suffered heart attacks but a post-mortem revealed they were injected with insulin.

Crown prosecutor Brendan Campbell said staff noticed insulin was missing from the medication room in the wing where Ms Spencer and Ms Darragh stayed.

"The only person that had access to the medication room was this accused," he said.

Ms Haines had been on her sixth night shift at St Andrews on May 9, 2014, after being employed a month prior.

The court heard on Wednesday that before Ms Haines walked through the doors of St Andrews her nursing career had been marred with difficulties.

Her nurse's registration in Victoria had been suspended after she was the subject of three misconduct investigations over as many years.

Despite this she was given the opportunity to work as a nurse again in 2012 but under strict reporting conditions that challenged her efforts to get a job, the court heard.

When Ms Haines began her shift on May 9, 2014, she learned she was the target of complaints again, this time from three residents.

The next morning, two of those elderly residents were dead.

The crown alleges the registered nurse was aware of the adverse impacts complaints could have had on her career having faced disciplinary hearings in the past.

Mr Campbell told the Supreme Court sitting in Lismore that Ms Haines had the opportunity and motive to kill the women.

"The crown says the accused injected them with the intention to kill them," he said.

Dressed in a navy suit and with her hair tied back, Ms Haines kept her hands clasped and stared towards the jury as details of the complaints made against her were detailed.

Mr Campbell explained that Ms Darragh had an itchiness condition, which nurses at the aged care home would apply cream for.

When Ms Darragh called for a nurse and pulled down her blanket, Ms Haines allegedly told her: "cover yourself up, you look disgusting".

Ms Spencer had complained that Ms Haines told her to "piss in her pad" when she asked for help to use the toilet, the court heard.

A third resident had alleged Ms Haines was "rough handed" with her.

However the defence submits that Ms Haines was not told that Ms Spencer was one of those who made a complaint.

The court heard that the nursing home director of care, Wendy Turner, informed Ms Haines on May 9, 2014 there would be a meeting to talk about the complaints the following Tuesday.

Ms Turner, the court heard, also made a point of reminding Ms Haines about the reporting conditions attached to her job.

After offering different explanations as to what happened with two of the residents, Ms Haines told her boss: "this has never happened to me before".

But Ms Haines had been at the centre of complaint probes in the past, the court heard.

In 2007 the Victorian nursing board found she had engaged in "unprofessional conduct of a serious nature" for failing to care for a patient at Box Hill Hospital, Mr Campbell said.

In July of that year, another complaint was made about Ms Haines sending text messages threatening to access patient information at Maroondah Hospital. It took four years for authorities to substantiate that complaint.

While the Maroondah case was being investigated, Ms Haines's nursing registration was suspended in 2008 after more complaints were made about her time at Caulfield Medical Centre.

Ms Haines's barrister Troy Edwards asked the jury to put aside any prejudice it had as a result of the Victoria complaints.

"She is not on trial for being insensitive to residents or being a bad nurse or even a bad person," he said.

Ms Haines was allowed to begin working as a nurse again from 2012 when authorities ticked off on her re-registration application.

The trial continues.